The present invention relates generally to microcircuits and more particularly to a xe2x80x9cGatling gunxe2x80x9d via, that is a via having a center conductor via surrounded by ground vias.
Today""s complex integrated circuits typically employ several million transistors on a single integrated circuit substrate. Multiple layers of conductive material are formed overlying the substrate in order for these millions of transistors to interconnect and work as a whole. To facilitate electrical communication between conductive layers, via structures are used. Vias are openings etched through dielectric layers between a first conductive layer and a second conductive layer.
Circuit board interconnects generally fall into three categories. The first category employs a laminated epoxy-filled cloth. The individual layers have electronically conductive paths of patterned copper. The second category uses a base structure of epoxy filled-cloth. This base is then covered with multiple layers of photoimageable dielectric and patterned copper. The third category is composed of multiple layers of laminated ceramic, with individually patterned copper. The present invention is directed to the formation of xe2x80x9cGatling gunxe2x80x9d vias with reference to the second category, although the concepts herein can apply to the other two interconnect schemes.
Vias can be formed by drilling holes and then plating the paths through the holes. The via holes can extend through the complete multilayer board. In this configuration, the vias are electrically coupled to each copper (i.e., conductive) layer. Alternatively, vias can be formed using a conventional photoimage-generated via structure.
One problem with via structures employed in high frequency applications is the lack of AC electrical isolation between the via and the remainder of the microcircuit. Another problem is that standard vias (formed either by drilling or by photoimaging) do not provide a controlled impedance environment at high frequencies.
The present invention provides a xe2x80x9cGatling gunxe2x80x9d via to interconnect circuitry from a first side of a substrate or printed circuit board, to a second side of the substrate or board. The present via comprises a center conductor via surrounded by a plurality of ground vias. The plurality of ground vias shield the center conductor via, thus providing electrical isolation for the conductor via from the rest of the circuitry. One feature of the present invention is that the plurality of ground vias can be modified, adjusting their diameters and their placement relative to the center conductor via, in order to affect the overall characteristic impedance of the Gatling gun via. This feature is useful when propagating high frequency signals from the first side to the second side of the substrate.